1. Field of the Invention
The present invention relates to a microwave plasma treatment apparatus, more particularly, to a microwave plasma treatment apparatus suitable for ashing treatment of semiconductor substrate.
2. Description of the Prior Art
The prior art on microwave plasma treatment apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 63-122123 (1988). The apparatus comprises a reflecting terminal having a plurality of small holes attached to a bottom side opening of a circular wave guide tube which forms a plasma generating chamber and is connected to a treatment chamber having a sample table, and a discharge tube having a concave surface being in parallel relationship with the sample table attached to an upper side opening of the circular wave guide tube which is connected to a wave guide tube for microwave. In order to generate high efficient plasma, the distance between the reflecting terminal and the discharge tube is made to be larger than one-eighth of the guide wave length of microwave. And in order to perform homogeneous ashing treatment throughout a wafer, the reflecting terminal is placed in parallel relationship with the wafer. Thus, the wafer is treated uniformly in a short time.
In the prior art described above, however, the control of microwave inside the wave guide tube is not taken into consideration, the microwave guiding efficiency into the plasma generating chamber is not sufficiently high, and the ashing treatment speed and the ashing treatment speed uniformity over the surface are not sufficient.